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Effects of alpha-amanitin on the transcription of the NOR of polytene chromosomes of Phaseolus coccineus embryo suspensor during embryogenesis



Effects of alpha-amanitin on the transcription of the NOR of polytene chromosomes of Phaseolus coccineus embryo suspensor during embryogenesis



Cytobios 98(387): 7-15



Nucleolar organizer regions (NOR) of polytene chromosomes of the Phaseolus coccineus suspensor are functionally and structurally heterogeneous. In order to investigate whether this heterogeneity is due, apart from the activity of ribosomal genes, to the activity of non-ribosomal genes, the incorporation of (3H)-uridine in suspensors treated with alpha-amanitin, a specific inhibitor of polymerases II and III, was investigated at different stages of embryogenesis. In two specific stages of embryo-genesis the alpha-amanitin treatment caused a reduction of (3H)-uridine incorporation in the NOR of chromosomes pairs II and V and no difference in the incorporation into the NOR of chromosome pair I. At a particular stage chromosome pair I showed an enhanced (3H)-uridine incorporation after alpha-amanitin treatment. The results demonstrate the presence and the activity of non-ribosomal genes in the NOR of chromosome pairs II and V and a different complexity of the chromatin in the NOR of chromosome pairs I, as compared with all other NOR. The data are discussed in relation to the chromatin organization of the NOR and to the functional heterogeneity of the ribosomal cistrons during embryogenesis.

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Accession: 010544972

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